Control system for vehicle

ABSTRACT

A control system is for a vehicle (Ve), and the control system comprises an electronic control unit ( 18 ). The electronic control unit ( 18 ) is configured to (i) produce differential rotation by controlling a rotational speed of either a first clutch member ( 24 ) or a second clutch member ( 25 ) of a selectable one-way clutch ( 17 ) by a motor ( 2 ), and (ii) execute the following processes in an order of (1.) to (4.) in the case where the electronic control unit ( 18 ) switches the selectable one-way clutch ( 17 ) from a disengaged state to a engaged state: (1.) controlling the motor ( 2 ) such that the differential rotation becomes the negative differential rotation; (2.) switching the selectable one-way clutch ( 17 ) from a second state to a first state; (3.) controlling the motor ( 2 ) such that the differential rotation becomes the positive differential rotation; and (4.) engaging a part of a strut with a part of the second clutch member ( 25 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a national phase application based on the PCT InternationalPatent Application No. PCT/IB2015/000550 filed Apr. 22, 2015, claimingpriority to Japanese Patent Application No. 2014-090866 filed Apr. 25,2014, the entire contents of both of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a system for controlling a mechanism thattransmits power for a travel of a vehicle. The invention particularlyrelates to a control system for a power transmission mechanism thatincludes a selectable one-way clutch.

2. Description of Related Art

The invention related to a vehicular transmission that includes aselectable one-way clutch (hereinafter described as an SOWC) isdescribed in US 2009/0084653 A. The SOWC described in this US2009/0084653 A includes: a first ring and a second ring that arearranged to face each other; and a strut that is arranged between thesefirst ring and second ring. The first ring is provided with a pocketwhich a tip of the strut enters and is engaged with. The second ring isprovided with a through opening. The strut is housed in the throughopening. The strut is configured to be pushed out to the pocket side bya projecting tooth of an apply ring via a spring, the projecting toothof the apply ring being inserted in the through opening from a backsurface side of the second ring (an opposite side of a surface thatfaces the first ring). A combination of the strut and the pocket isprovided in two types that are a first type and a second type. In thefirst type, the strut and the pocket are engaged when the SOWC transmitstorque in a forward travel direction. In the second type, the strut andthe pocket are engaged when the SOWC transmits the torque in a reversetravel direction. A blocking device is arranged between the first ringand the second ring in a manner to rotate within a specified anglerange. The blocking device is a ring-shaped plate like the first ringand the second ring. This blocking device is provided with a windowthrough which the strut passes. In addition, a return mechanism thatpresses the blocking device in a direction to separate the blockingdevice from the first ring is provided between the blocking device andthe first ring. Then, the above apply ring is configured to be moved byan actuator in a rotational axis direction. Accordingly, it isconfigured that the second ring and the blocking device are pressed tothe first ring side via the apply ring and the projecting tooth bypressing the apply ring to the first ring side by thrust of theactuator.

In a disengaged state in which the above SOWC is not engaged in any ofrotational directions of the forward travel direction and the reversetravel direction, the strut is pressed in the through opening of thesecond ring by the blocking device. In other words, the first ring iscompletely separated from the blocking device and the second ring. Theactuator is actuated in such a disengaged state to press the second ringand the blocking device to the first ring side. As a result, theblocking device is brought into contact with an opposing surface of thefirst ring. The blocking device that is in contact with the first ringrotates in a rotational direction of the first ring by a friction forcethat is generated at this time. Then, when a position of the window ofthe blocking device matches a position of the through opening of thesecond ring (that is, the strut) in the rotational direction, the strutis pushed out from the window to the first ring side. As a result, thetip of the strut is engaged with the pocket that is formed in the firstring. In other words, the SOWC is switched to an engaged state.

Noted that the invention related to an SOWC is described in US2013/0062151 A. The SOWC is constructed of: a strut; a notch plate thatis formed with a notch, the notch being engaged with the strut; a pocketplate that is provided with a recess section for housing the strut; acontrol plate that is formed with an opening through which the strutpasses and that controls an engaged state between the strut and thenotch.

In the SOWC described in US 2009/0084653 A above, in the case where theSOWC is switched from a disengaged state (MODE 1) to an engaged state(MODE 2), the SOWC is controlled such that a negative difference(differential rotation) is once produced between a rotational speed ofthe first plate and a rotational speed of the second plate. Thereafter,the SOWC is controlled such that a differential rotation speed becomespositive. The SOWC is switched from the disengaged state to the engagedstate in a state that the differential rotation speed has actuallybecome positive. In other words, the blocking device is brought intocontact with the first ring for rotation. The tip of the strut, which isprojected from the window of the blocking device, is engaged with thepocket of the first ring. In this way, the SOWC is switched from thedisengaged state to the engaged state. At this time, a time lag isgenerated between an operation of the blocking device and an operationof the strut. Accordingly, the SOWC is switched to the engaged stateafter a specified time period has elapsed since the differentialrotation speed thereof becomes positive. Noted that, in this SOWC, astate of a positive differential rotation corresponds to a direction inwhich the strut and the pocket are engaged. The state of the positivedifferential rotation corresponds to a rotational state in which thetorque can be transmitted between the first ring and the second ring. Astate of the negative differential rotation corresponds to the directionin which the strut and the pocket are not engaged. The state of thenegative differential rotation corresponds to the rotational state inwhich the torque is not transmitted between the first ring and thesecond ring.

Just as described, in the SOWC described in US 2009/0084653 A, the strutand the pocket are engaged when the differential rotation speed ispositive. In addition, as described above, the SOWC can transmit thetorque when the differential rotation speed is positive. Accordingly,there is a case where a load is applied to the strut, which is pressedto the pocket side, immediately after the strut enters the pocket.Regarding this problem, in this SOWC described in US 2009/0084653 A, theblocking device for controlling an operation of the strut is indirectlyoperated, that is, operated by following an operation of any othercomponent of the SOWC. In other words, the SOWC is not configured thatthe operation of the blocking device is actively controlled.Accordingly, there is a case where the strut and the pocket are engagedat an improper position as described in this US 2009/0084653 A. Theimproper position refers to a position that is located in a middle of apath for the strut to be engaged at a specified position in the pocket.If the strut is engaged at such an improper position, an area of acontact portion between the strut and the pocket is reduced. Thus,surface pressure of the contact portion is increased. As a result,durability of the SOWC is possibly degraded.

SUMMARY OF THE INVENTION

The invention provides a control system for a vehicle with which aselectable one-way clutch can appropriately be engaged.

A first aspect of the invention is a control system for a vehicle. Thecontrol system includes a selectable one-way clutch, a motor, and anelectronic control unit. The selectable one-way clutch includes a firstclutch member, a second clutch member, a strut, and a switchingmechanism. The first clutch member and the second clutch member areconfigured to rotate relatively to each other. At least a part of thestrut is configured to be operated such that the part of the strut isprojected from the first clutch member side to the second clutch memberside. The switching mechanism is configured to selectively set a firststate and a second state. The first state is a state that the switchingmechanism permits projection of the strut from the first clutch memberside to the second clutch member side. The second state is a state thatthe switching mechanism inhibits the projection of the strut. Theselectable one-way clutch is configured to be switched between anengaged state and a disengaged state. The engaged state is a state thatrestricts the relative rotation in either a positive rotationaldirection or a reverse rotational direction in the first state that thepart of the strut is projected from the first clutch member side to thesecond clutch member side and is engaged with a part of the secondclutch member. The disengaged state is a state that permits the relativerotation in the positive rotational direction and the relative rotationin the reverse rotational direction in the second state that the strutis not projected to the second clutch member side. The motor isconfigured to control a rotational speed of either the first clutchmember or the second clutch member. The electronic control unit isconfigured to produce differential rotation by controlling therotational speed by the motor. The differential rotation includespositive differential rotation and negative differential rotation. Thepositive differential rotation is the relative rotation in which therelative rotation is restricted in the engaged state. The negativedifferential rotation is the relative rotation in which the relativerotation is permitted in the engaged state. The electronic control unitis configured to execute the following processes in an order of (1) to(4) in the case where the electronic control unit switches theselectable one-way clutch from the disengaged state to the engagedstate: (1) controlling the motor such that the differential rotationbecomes the negative differential rotation; (2) switching from thesecond state to the first state such that the part of the strut isprojected from the first clutch member side to the second clutch memberside in a state that the differential rotation is the negativedifferential rotation; (3) controlling the motor such that thedifferential rotation becomes the positive differential rotation; and(4) engaging the part of the strut with the part of the second clutchmember in a state that the differential rotation is the positiverotational direction.

According to the above aspect, in the case where the selectable one-wayclutch is switched from the disengaged state to the engaged state,rotation of the motor is controlled such that the differential rotationspeed of the selectable one-way clutch becomes negative. Then, theswitching mechanism is actuated such that the strut can be projected tothe position which is between the two clutch members and at which thestrut can be engaged (the first state) in the state that thedifferential rotation speed is negative. When the differential rotationspeed of the selectable one-way clutch is positive, the torque can betransmitted between the two clutch members. Accordingly, a load ispossibly applied to the strut. On the contrary, when the differentialrotation speed is negative, the torque is not transmitted between thetwo clutch members. Accordingly, no load is applied to the strut, andthe strut can easily be operated. Thus, by setting the first state asdescribed above in the state that the differential rotation speed isnegative, the strut can easily be operated and reliably be engaged at aspecified position. Therefore, the selectable one-way clutch in thedisengaged state can reliably and appropriately be switched to theengaged state.

In the above aspect, first target differential rotation speed may be setas a target value of the differential rotation speed that is used whenthe electronic control unit controls the motor such that thedifferential rotation becomes the negative differential rotation. Theelectronic control unit may be configured to control the motor such thatthe differential rotation speed is maintained at the first targetdifferential rotation speed until the part of the strut is projected tothe second clutch member side.

According to the above aspect, in the case where the differentialrotation speed of the selectable one-way clutch is brought into thenegative state as described above, the rotation of the motor iscontrolled such that the differential rotation speed is maintained atthe first target differential rotation speed that is set as a value onthe negative side. When the differential rotation speed is controlled,control disturbance or a fluctuation in control occurs due to afluctuation in torque of the engine, input of disturbance torque, or thelike, for example. For this reason, the first target differentialrotation speed as described above is set in consideration of suchcontrol disturbance or such a fluctuation in the control. Thus, thestrut can be operated in a state that the differential rotation speed isreliably negative. In other words, the strut can be operated in a statethat the load is never applied to the strut. Thus, the strut can easilybe operated and reliably be engaged at the specified position.

In the above aspect, the switching mechanism may include an actuatorthat is configured to operate the strut. After the electronic controlunit controls the motor such that the differential rotation becomes thenegative differential rotation, the electronic control unit sets thefirst state in the state that the differential rotation is the negativedifferential rotation. In such a case, the electronic control unit maybe configured to initiate actuation of the actuator before thedifferential rotation speed reaches the first target differentialrotation speed.

According to the above aspect, in the case where the differentialrotation speed of the selectable one-way clutch is maintained at thefirst target differential rotation speed that is set as the value on thenegative side, the actuator starts being actuated to operate the strutbefore the differential rotation, which is controlled to become thefirst target differential rotation speed, reaches the first targetdifferential rotation speed. For this reason, time required forswitching of the selectable one-way clutch to the engaged state can beshortened.

In the above aspect, the switching mechanism may include an actuatorthat is configured to operate the strut. After the electronic controlunit controls the motor such that the differential rotation becomes thenegative differential rotation, the electronic control unit sets thefirst state in the state that the differential rotation is the negativedifferential rotation. In such a case, the electronic control unit maybe configured to initiate the actuation of the actuator when thedifferential rotation speed is zero or the positive value that is closeto zero.

According to the above aspect, in the case where the differentialrotation speed of the selectable one-way clutch is maintained at thefirst target differential rotation speed that is set as the value on thenegative side, the actuator starts being actuated to operate the strutwhen the differential rotation speed, which is controlled to become thefirst target differential rotation speed, is zero or a positive valuethat is close to zero. Thus, the strut can be operated and engaged in astate that the differential rotation speed is close to zero, at whichthe strut is less likely to be influenced by inertia torque. Therefore,shock received by the strut during the engagement can be suppressed. Inaddition, since the actuator starts being actuated before thedifferential rotation speed reaches the first target differentialrotation speed, the time required for switching of the selectableone-way clutch to the engaged state can be shortened.

In the above aspect, the switching mechanism may include the actuatorthat is configured to operate the strut. The first target differentialrotation speed may be set as the target value of the differentialrotation speed that is used when the electronic control unit controlsthe motor such that the differential rotation becomes the negativedifferential rotation. Second target differential rotation speed may beset as a target value of the differential rotation speed that is usedwhen the electronic control unit controls the motor such that thedifferential rotation becomes the positive differential rotation. Theelectronic control unit may be configured to execute the followingprocesses in an order of (i) to (v): (i) actuating the actuator to setthe first state such that the part of the strut is projected to thesecond clutch member side in the state that the differential rotationspeed is maintained at the first target differential rotation speed;(ii) then, controlling the motor by the electronic control unit suchthat the differential rotation becomes the positive differentialrotation; (iii) engaging the part of the strut with the part of thesecond clutch member in the state that the differential rotation is thepositive differential rotation; (iv) controlling the motor after theactuation of the actuator is completed and an operation of the part ofthe strut to be projected to the second clutch member side is completed,such that the differential rotation speed is increased to the secondtarget differential rotation speed; and (v) controlling the motor suchthat the differential rotation speed is maintained at the second targetdifferential rotation speed until engagement of the part of the strutand the part of the second clutch member is completed.

According to the above aspect, in the case where the differentialrotation speed of the selectable one-way clutch is maintained at thefirst target differential rotation speed, which is set as the value onthe negative side, timing for starting the actuator operation or forincreasing the differential rotation speed to the positive side so as toengage the selectable one-way clutch and thus to transmit the torque, isset in consideration of time at which the actuation of the actuator orthe operation of the strut is completed. Then, also in the case wherethe differential rotation speed of the selectable one-way clutch that isbrought into the negative state as described above becomes positive, thetime at which the actuator starts being actuated or the time forincreasing the differential rotation speed to the positive side, so asto engage the selectable one-way clutch and thus to transmit the torque,is set. Therefore, the selectable one-way clutch in the disengaged statecan reliably and appropriately be switched to the engaged state.

In the above aspect, an absolute value of the first target differentialrotation speed may be set higher as a magnitude of predicted controldisturbance is increased.

According to the above aspect, as described above, when the differentialrotation speed is controlled, the control disturbance or the fluctuationin control occurs due to the fluctuation in torque of the engine, theinput of disturbance torque, or the like, for example. In this case, thefirst target differential rotation speed is set such that the absolutevalue of the first target differential rotation speed becomes higher asa magnitude of such control disturbance is increased. Accordingly, thestrut can be operated in a state that the load is never applied to thestrut.

In the above aspect, an internal combustion engine, a drive wheel, and apower transmission may further be provided. The power transmissionmechanism may include a fixed section and a first differentialmechanism. Either the first clutch member or the second clutch membermay be coupled to the fixed section. The fixed section may be configurednot to rotate or move. The first differential mechanism may include afirst rotary element, a second rotary element, and a third rotaryelement. The first rotary element, the second rotary element, and thethird rotary element may be configured to perform a differential actionwith respect to each other. The internal combustion engine may becoupled to the first rotary element. The motor and the other of thefirst clutch member or the second clutch member may be coupled to thesecond rotary element. The first differential mechanism may beconfigured to output torque from the third rotary element to the drivewheel.

In the above aspect, the internal combustion engine, the drive wheel,and the power transmission may further be provided. The powertransmission mechanism may include the fixed section, the firstdifferential mechanism, and a second differential mechanism. Either thefirst clutch member or the second clutch member may be coupled to thefixed section. The fixed section may be configured not to rotate ormove. The first differential mechanism may include the first rotaryelement, the second rotary element, and the third rotary element. Thefirst rotary element, the second rotary element, and the third rotaryelement may be configured to perform a differential action with respectto each other. The internal combustion engine may be coupled to thefirst rotary element. The motor may be coupled to the second rotaryelement. The first differential mechanism may be configured to outputtorque from the third rotary element to the drive wheel. The seconddifferential mechanism may include a fourth rotary element, a fifthrotary element, and a sixth rotary element. The fourth rotary element,the fifth rotary element, and the sixth rotary element may be configuredto perform the differential action with respect to each other. The firstrotary element may be coupled to the fourth rotary element. The secondrotary element may be coupled to the fifth rotary element. The other ofthe first clutch member or the second clutch member may be coupled tothe sixth rotary element. In the second differential mechanism, thefifth rotary element may be configured to rotate in an oppositedirection from a rotational direction of the fourth rotary element bystopping a rotation of the sixth rotary element.

The above aspect can be applied to the control device for the powertransmission mechanism in which a speed of the internal combustionengine can be controlled by the motor via the differential mechanism. Inthis case, the selectable one-way clutch can selectively restrictrotation of any of the rotary elements of the differential mechanism ina specified direction. Then, the selectable one-way clutch can reliablyand appropriately be switched from the disengaged state to the engagedstate.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a view of an example of a configuration of a powertransmission mechanism in a hybrid vehicle to which the invention isapplied;

FIG. 2 includes collinear diagrams on a planetary gear mechanism thatconstitutes the power transmission mechanism in the hybrid vehicle shownin FIG. 1;

FIG. 3 is a view of another example of the configuration of the powertransmission mechanism in the hybrid vehicle to which the invention isapplied;

FIG. 4 includes collinear diagrams on a compound planetary gearmechanism that constitutes a power split mechanism and an overdrivemechanism in the hybrid vehicle shown in FIG. 3;

FIG. 5 is a cross-sectional view of a configuration of a selectableone-way clutch that can be a subject of the invention;

FIG. 6 is a view of a housing section and a pocket, the housing sectionbeing formed in a first clutch plate and the pocket being formed in asecond clutch plate of the selectable one-way clutch shown in FIG. 5;

FIG. 7 is a flowchart for illustrating an example of control that isexecuted by a control device of the invention;

FIG. 8A is a diagram for illustrating an example of the map that isapplied when the control shown in the flowchart in FIG. 7 is executed;

FIG. 8B is a diagram for illustrating an example of the map that isapplied when the control shown in the flowchart in FIG. 7 is executed;

FIG. 9 is a time chart that shows an example of a change in differentialrotation speed of the selectable one-way clutch when the control shownin the flowchart of FIG. 7 is executed;

FIG. 10 is a view of yet another example of the configuration of thepower transmission mechanism in the hybrid vehicle to which theinvention is applied; and

FIG. 11 includes collinear diagrams on the planetary gear mechanism thatconstitutes the power split mechanism in the hybrid vehicle shown inFIG. 10.

DETAILED DESCRIPTION OF EMBODIMENTS

Next, a specific description will be made on the invention withreference to the drawings. The invention can be applied to a controlsystem of which a power transmission mechanism in a hybrid vehicle is asubject. First, an example of a configuration of the power transmissionmechanism will be described. FIG. 1 schematically shows the powertransmission mechanism in a hybrid vehicle Ve of double-spindletwo-motor type. The hybrid vehicle Ve includes: an engine (Eng) 1 as anexample of an internal combustion engine of the invention; a first motor(MG1) 2 an example of a motor of the invention; and a second motor (MG2)3 as drive power sources.

The first motor 2 is configured to mainly execute control of a speed ofthe engine 1 and cranking of the engine 1. This first motor 2 is alsoconfigured to function as one of the drive power sources in a two-motortravel mode (a two-motor EV mode) in which a vehicle travels by the twomotors. Together with the engine 1, the first motor 2 is coupled to apower split mechanism 4 that is an example of the first differentialmechanism of the invention.

In this example shown in FIG. 1, the power split mechanism 4 isconstructed of a planetary gear mechanism of single pinion type thatincludes a sun gear 5, a carrier 6, and a ring gear 7 as rotaryelements. A rotor of the first motor 2 is coupled to the sun gear 5 thatis an example of a second rotary element of the invention among therotary elements. In addition, an output shaft (a crankshaft) of theengine 1 is coupled to the carrier 6 that is an example of a firstrotary element of the invention. The ring gear 7 that is an example of athird rotary element of the invention is an output element. An outputgear 8 as an output member is attached to the ring gear 7. The outputgear 8 meshes with a counter driven gear 9. The counter driven gear 9 isattached to a counter shaft 10. A counter drive gear 11 that has asmaller diameter than the counter driven gear 9 is attached to thecounter shaft 10. The counter drive gear 11 meshes with a ring gear 13in a differential gear 12. Then, the differential gear 12 outputs drivetorque to right and left drive wheels 14.

The second motor 3 is configured to mainly function as a drive powersource for a travel. A drive gear 15 is attached to a rotor shaft of thesecond motor 3. The drive gear 15 meshes with the counter driven gear 9.This drive gear 15 has a smaller diameter than the counter driven gear9. In this manner, the drive gear 15 and the counter driven gear 9constitute a speed reduction mechanism.

A selectable one-way clutch (hereinafter described as an SOWC) 17 isprovided between the sun gear 5, to which the first motor 2 is coupled,and a casing 16 that is an example of a fixed section of the invention.This SOWC 17 is a clutch that is configured to enable relative rotationin both directions of positive rotation and reverse rotation so as toprevent torque transmission in a disengaged state. This SOWC 17 is aclutch that is configured to restrict the relative rotation in only onedirection of the positive rotation and the reverse rotation so as totransmit the torque in the direction of the relative rotation and toenable the relative rotation in an opposite direction therefrom, so asto prevent the torque transmission in an engaged state. Here, thepositive rotation refers to rotation in the same direction as arotational direction of the engine 1. This rotational direction refersto a positive rotational direction. The reverse rotation (or negativerotation) refers to rotation in an opposite direction from therotational direction of the engine 1. This rotational direction refersto a reverse rotational direction. In addition, similar to the SOWCdescribed in above-described US 2009/0084653 A, this SOWC 17 isconfigured to be able to transmit the torque when a difference in therotational speed (differential rotation) between the two rotary membersthat are involved in torque transmission, that is, between a firstclutch plate 24 and a second clutch plate 25, which will be describedbelow, is positive. This SOWC 17 is configured not to transmit thetorque when the differential rotation speed is negative. Noted that thespecific configuration of this SOWC 17 will be described below.

The first motor 2 and the second motor 3 are connected to an electricalstorage device and a controller unit such as an inverter, which are notshown. In addition, the motors 2, 3 are electrically connected to eachother to enable electrical power transfer therebetween. Furthermore, anelectronic control unit (ECU) 18 is provided to control these electricalstorage device and controller unit, the SOWC 17, or the like. Thiselectronic control unit 18 is constructed of a microcomputer as a mainbody. This electronic control unit 18 is configured to receive detectionsignals indicative of a vehicle speed, an accelerator operation amount,an engine speed, estimated output torque, a rotational speed and torqueof each of the motors 2, 3, an operating state of the SOWC 17, and thelike as data. In addition, this electronic control unit 18 is configuredto output command signals for controlling each of the motors 2, 3 andthe SOWC 17, the command signals being obtained by performingcomputation based on the input data.

FIG. 2 includes collinear diagrams on the planetary gear mechanism thatconstitutes the above power split mechanism 4. A top diagram in FIG. 2indicates a forward traveling state in a hybrid mode (an HV mode or apower split mode). In this state shown in the top diagram in FIG. 2, theengine 1 is driven, and thus the carrier 6 rotates in the positiverotational direction. In addition, due to the forward travel of thevehicle Ve, the ring gear 7 rotates in the positive rotationaldirection. At this time, the SOWC 17 is disengaged, and thus the sungear 5 and the first motor 2, which is coupled to the sun gear 5, canrotate in either direction of the positive rotation or the reverserotation. In this state shown in the top diagram in FIG. 2, the firstmotor 2 functions as an electrical power generator while making thepositive rotation. In other words, the first motor 2 outputs torque in anegative direction (a downward direction in the top diagram in FIG. 2)and thereby controls the speed of the engine 1 to a speed at whichexcellent fuel efficiency can be realized. In this case, the electricalpower generated in the first motor 2 is supplied to the second motor 3.Then, the second motor 3 functions as the motor and outputs drive powerfor the travel.

A second diagram from the top in FIG. 2 indicates a transient state (atransition state) in which the SOWC 17 is switched between the stateshown in the top diagram in FIG. 2 and a state shown in the thirddiagram from the top in FIG. 2, which will be described below. In otherwords, the second diagram from the top in FIG. 2 indicates a transientstate when the SOWC 17 is switched from the disengaged state (free) tothe engaged state (locked) in which the positive rotation of the sungear 5 is stopped. In this state shown in the second diagram from thetop in FIG. 2, the first motor 2 functions as the motor and rotates thesun gear 5 in a reverse rotational direction. As a result, the negativedifferential rotation is produced in the SOWC 17. In other words, theSOWC 17 does not transmit the torque. Thus, when the engagement controlof the SOWC 17 is executed in this state, the torque is not applied tothe strut 26 of the SOWC 17, which will be described below.

A third diagram from the top in FIG. 2 indicates a state in which thepositive rotation of the sun gear 5 is stopped by the SOWC 17 and inwhich the vehicle travels forward by the drive power of the engine 1 orby the drive power of the engine 1 and the drive power of the secondmotor 3 (in a so-called parallel mode). In this state shown in the thirddiagram from the top in FIG. 2, a rotational speed of the ring gear 7 ishigher than the engine speed (a rotational speed of the carrier 6), andthus the torque is output from the ring gear 7. When the second motor 3is operated as the motor in this state, the drive power thereof is addedto the drive power that is output from the ring gear 7 and istransmitted to the drive wheels 14 via the differential gear 12. Also inthis case, the first motor 2 and the sun gear 5 are fixed, andenergization thereof is stopped (in an OFF state). Thus, the excellentfuel efficiency can be realized when the vehicle travels at a highspeed.

FIG. 3 shows another example of the configuration of the powertransmission mechanism that can be the subject of the invention. In thisconfiguration shown in FIG. 3, an overdrive (O/D) mechanism 19 is addedto the above-described configuration shown in FIG. 1. This configurationshown in FIG. 3 is also an example of the configuration in which theoverdrive mechanism 19 is selectively locked by the SOWC 17. Theoverdrive mechanism 19 is an example of a second differential mechanismof the invention. In this example shown in FIG. 3, the overdrivemechanism 19 is constructed of a planetary gear mechanism of doublepinion type that includes a sun gear 20, a carrier 21, and a ring gear22 as rotary elements. The carrier 6 in the above-described power splitmechanism 4 is coupled to the carrier 21 that is an example of a fourthrotary element of the invention. Accordingly, it is configured that theoutput torque of the engine 1 is transmitted to these carrier 6 andcarrier 21. In addition, the sun gear 5 in the power split mechanism 4is coupled to the sun gear 20 that is an example of a fifth rotaryelement of the invention. Accordingly, it is configured that the torqueof the first motor 2 is transmitted to these sun gear 5 and sun gear 20.Furthermore, the above-described SOWC 17 is arranged between the casing16 and the ring gear 22 that is an example of a sixth rotary element ofthe invention. It is configured that the SOWC 17 restricts (inhibits)rotation of the ring gear 22 in a specified direction, so as to set anoverdrive state. The rotary elements of the planetary gear mechanism ofthe single pinion type that constitutes the power split mechanism 4 andthe rotary elements of the planetary gear mechanism of the double piniontype that constitutes the overdrive mechanism 19 are coupled asdescribed above. In this way, a so-called compound planetary gearmechanism having the four elements is constructed. Since the rest of theconfiguration of the power transmission mechanism is the same as theconfiguration shown in FIG. 1, components shown in this FIG. 3 aredenoted by the same reference numerals as those used in FIG. 1, and thedescription thereof will not be made.

FIG. 4 includes collinear diagrams on the above compound planetary gearmechanism, and a top diagram in FIG. 4 indicates the forward travelingstate in the hybrid mode (the HV mode or the power split mode). In thisstate shown in the top diagram in FIG. 4, the engine 1 is driven, andthus the carrier 6 rotates in the positive rotational direction. Inaddition, due to the forward travel of the vehicle Ve, the ring gear 7rotates in the positive rotational direction. At this time, the SOWC 17is disengaged, and thus the sun gear 5 or the ring gear 22, and thefirst motor 2, which can rotate the sun gear 5 and the ring gear 22, canrotate in either direction of the positive rotation or the reverserotation. In this state shown in the top diagram in FIG. 4, the firstmotor 2 functions as an electrical power generator while making thepositive rotation. In other words, the first motor 2 outputs the torquein a negative direction (a downward direction in the top diagram in FIG.4) and thereby controls the speed of the engine 1 to the speed at whichthe excellent fuel efficiency can be realized. In this case, theelectrical power generated in the first motor 2 is supplied to thesecond motor 3. Then, the second motor 3 functions as the motor andoutputs the drive power for the travel.

A second diagram from the top in FIG. 4 indicates a transient state (atransition state) in which the SOWC 17 is switched between the stateshown in the top diagram in FIG. 4 and a state shown in the thirddiagram from the top in FIG. 4, which will be described below. In otherwords, the second diagram from the top in FIG. 4 indicates a transientstate when the SOWC 17 is switched from the disengaged state (free) tothe engaged state (locked) in which the SOWC 17 stops the positiverotation of the ring gear 22. In this state shown in the second diagramfrom the top in FIG. 4, the first motor 2 functions as the motor androtates the sun gear 5 or the ring gear 22 in the reverse rotationaldirection. The rotational speed at this time is the rotational speed atwhich the ring gear 22 rotates in the reverse rotational direction, andthe negative differential rotation is produced in the SOWC 17. In otherwords, the SOWC 17 does not transmit the torque. Thus, when theengagement control of the SOWC 17 is executed in this state, the torqueis not applied to the strut 26 of the SOWC 17, which will be describedbelow.

A third diagram from the top in FIG. 4 indicates a state in which thepositive rotation of the ring gear 22 is stopped by the SOWC 17 and inwhich the vehicle travels forward by the drive power of the engine 1 orby the drive power of the engine 1 and the drive power of the secondmotor 3. In this state shown in the third diagram from the top in thisFIG. 4, the ring gear 22 in the overdrive mechanism 19 is fixed so asnot to rotate in the positive rotational direction. Then, torque in thepositive rotational direction is applied to the carrier 21. Accordingly,the sun gear 20 rotates in the reverse rotational direction. In thepower split mechanism 4, the sun gear 5 is integrated with the sun gear20 in the overdrive mechanism 19 and rotates in the reverse rotationaldirection. Accordingly, in the power split mechanism 4, since the torqueof the engine 1 is applied to the carrier 6 in the state that the sungear 5 rotates in the reverse rotational direction, the ring gear 7 asthe output element rotates at the higher rotational speed than thecarrier 6 (that is, the engine 1). In other words, the overdrive stateis generated. When the second motor 3 is operated as the motor in thisstate, the drive power thereof is added to the drive power that isoutput from the ring gear 7 and is transmitted to the drive wheels 14via the differential 12. Noted that, in this overdrive state, the firstmotor 2 is fixed with the ring gear 22 and controlled to be in the OFFstate. Thus, the excellent fuel efficiency can be realized when thevehicle travels at a high speed.

Here, the configuration of the SOWC 17 will be described. In the powertransmission mechanism that is the subject of the invention, forexample, the SOWC that is described in above-described US 2009/0084653A, the SOWC that is described in above-described US 2013/0062151 A, anSOWC that is described in US 2010/0252384 A, or the like can be adopted.Furthermore, the SOWC 17 that is configured as shown in FIG. 5 and FIG.6 can be adopted. These FIG. 5 and FIG. 6 show an engagement mechanism23 in the SOWC 17. This engagement mechanism 23 is mainly constructed ofthe first clutch plate 24, the second clutch plate 25, a strut 26, andan actuation mechanism 27.

The first clutch plate 24 is formed in a disc shape as a whole. Thesecond clutch plate 25 that is also formed in the disc shape as thefirst clutch plate 24 is arranged to face this first clutch plate 24. Ofthese clutch plates 24, 25, the first clutch plate 24 is an example of afirst clutch member of the invention. Of these clutch plates 24, 25, thesecond clutch plate 25 is an example of a second clutch member of theinvention. These clutch plates 24, 25 are retained to enable relativerotation to each other. For example, the one clutch plate 24 (25) isattached to the above-described casing 16. The other clutch plate 25(24) is coupled to the sun gear 5 in the example shown in FIG. 1.Alternatively, in the example shown in FIG. 3, the other clutch plate 25(24) is coupled to the ring gear 22.

The first clutch plate 24 is provided with a recessed section that iselongated in a rotational direction at a position that is in a frontsurface of the first clutch plate 24 and that is shifted to a radiallyouter side from the center of rotation of the first clutch plate 24,that is, at a specified position on an outer peripheral side. Thisrecessed section is a housing section 28 for housing the strut 26. Thesecond clutch plate 25 is provided with a pocket 29 that is a recessedsection in the substantially same shape as the housing section 28 at aradial position that is in a surface of the second clutch plate 25facing the first clutch plate 24 and that corresponds to the housingsection 28. A plate-shaped engagement piece whose cross section issubstantially the same as that of the housing section 28, that is, thestrut 26 is housed in the housing section 28. The strut 26 is arrangedin the housing section 28 in a manner to swing with a support pin 30being the center, the support pin 30 being provided at the center in alongitudinal direction of the strut 26 and facing the radial directionof the first clutch plate 24. A depth of the recessed section of thehousing section 28 is changed at the support pin 30. More specifically,an upper half of the housing section 28 in FIG. 5 has a thickness thatis substantially equal to a thickness of the strut 26 or that isslightly larger than the thickness of the strut 26. Then, a lower halfof the housing section 28 in FIG. 5 has a thickness that is larger thanthe thickness of the strut 26. In this way, the strut 26 is configuredto be able to swing with the support pin 30 being the center.

A spring 31 that causes an elastic force to act in a direction to pushout one end side of the strut 26 from the housing section 28 is arrangedin a shallow portion of the housing section 28. In addition, an actuator32 that presses another end side of the strut 26 in the direction topush out from the housing section 28 is arranged in a deep portion ofthe housing section 28. This actuator 32 only needs to be able to applya pressing force to the other end side of the strut 26. For example, ahydraulic actuator such as a hydraulic piston or an electromagneticactuator such as a solenoid that generates thrust by using anelectromagnetic force can be adopted. Accordingly, in a state that theactuator 32 does not press the other end of the strut 26, it isconfigured that the one end of the strut 26 is pressed by the spring 31and is projected from the housing section 28 toward the pocket 29 on thesecond clutch plate 25 side. In addition, in a state that the actuator32 presses the other end of the strut 26, it is configured that thestrut 26 rotates about the support pin 30 in a direction to compress thespring 31 and that the entire strut 26 is housed in the housing section28. In other words, it is configured to inhibit the strut 26 from beingprojected to the second clutch plate 25 side.

As described above, the spring 31 and the actuator 32 constitute theactuation mechanism 27 for operating the strut 26. Then, as describedabove, a state that the actuator 32 does not press the other end of thestrut 26 and that the one end of the strut 26 is pressed by the spring31 and projected from the housing section 28 toward the pocket 29 on thesecond clutch plate 25 side corresponds to a state that the projectionof the strut 26 to the second clutch plate 25 is permitted. That is,such a state is an example of the first state of the invention. Inaddition, a state that the actuator 32 presses the other end of thestrut 26, that the strut 26 rotates about the support pin 30 in adirection to compress the spring 31, and that the entire strut 26 ishoused in the housing section 28 corresponds to a state that theprojection of the strut 26 to the second clutch plate 25 side isinhibited. That is, such a state is an example of the second state ofthe invention. Accordingly, the actuation mechanism 27 for operating thestrut 26 by the above spring 31 and actuator 32 is an example of aswitching mechanism of the invention.

Noted that, in the above engagement mechanism 23, an appropriate elasticmember such as a spring may be interposed between the actuator 32 andthe other end of the strut 26 in order to relax the pressing forcegenerated by the actuator 32 or to permit swinging of the strut 26 inthe state that the actuator 32 presses the other end of the strut 26. Inaddition, the following description will be made on an example in whichit is configured that, when the actuator 32 is controlled to be OFF, theactuator 32 presses the other end of the strut 26 so as to bring theengagement mechanism 23 into a disengaged state. The followingdescription will further be made on an example in which it is alsoconfigured that, when the actuator 32 is controlled to be ON, theactuator 32 cancels pressing of the other end of the strut 26 so as tobring the engagement mechanism 23 into an engaged state.

As described above, the pocket 29 that is provided in the second clutchplate 25 is a portion which the one end of the strut 26 projected fromthe housing section 28 enters and is engaged with. Accordingly, in theengagement mechanism 23, in a state that the one end of the strut 26 isprojected to the second clutch plate 25 side, in the case where torquein the positive rotational direction acts on either one of the clutchplates 24, 25, the strut 26 is meshed between the housing section 28 andthe pocket 29. That torque in the positive rotational direction acts oneither one of the clutch plates 24, 25 means that torque in an upwarddirection of FIG. 5 acts on the first clutch plate 24 or that torque ina downward direction of FIG. 5 acts on the second clutch plate 25. As aresult, the clutch plates 24, 25 are integrally coupled in therotational direction. That is, the relative rotation of the first clutchplate 24 in the upward direction of FIG. 5 to the second clutch plate 25is restricted. In other words, the relative rotation of the secondclutch plate 25 in the downward direction of FIG. 5 to the first clutchplate 24 is restricted. The restricted rotational direction in this caseis the positive rotational direction in each of the power transmissionmechanisms shown in above-described FIG. 1 and FIG. 3. A state that thepositive rotation of the above-described sun gear 5 or ring gear 22 isrestricted (or inhibited), just as described, is the engaged state ofthe engagement mechanism 23 or the SOWC 17.

In the engaged state of the SOWC 17 as described above, in the casewhere the torque in the reverse rotational direction (the negativerotational direction) acts on either one of the clutch plates 24, 25,the surface of the strut 26 is pressed by an edge portion of an openingend of the pocket 29 in the second clutch plate 25. That the torque inthe reverse rotational direction (the negative rotational direction)acts on either one of the clutch plates 24, 25 means that the torque inthe downward direction of FIG. 5 acts on the first clutch plate 24 orthat the torque in the upward direction of FIG. 5 acts on the secondclutch plate 25. As a result, the strut 26 acts against the elasticforce of the spring 31 and is pushed in the housing section 28. In otherwords, the engagement by the strut 26 is canceled, and the clutch plates24, 25 can rotate relatively. Then, when the actuator 32 presses theother end of the strut 26, the strut 26 rotates in such a direction thatthe one end thereof enters the housing section 28 while compressing thespring 31. As a result, the strut 26 is housed in the housing section28. Accordingly, the member that connects the clutch plates 24, 25 nolonger exist, and thus the clutch plates 24, 25 can rotate relatively ineither direction of the positive rotation or the negative rotation. Thisstate is the disengaged state of the engagement mechanism 23, that is,the SOWC 17.

As described above, the engaged state and the disengaged state of theSOWC 17 are switched by the operation of the actuator 32. Accordingly,it is possible by detecting the operating state or an operation amountof the actuator 32 to determine whether the SOWC 17 is in the engagedstate or the disengaged state on the basis of the detection result. Forthis reason, the engagement mechanism 23 is provided with a strokesensor 33 for performing the detection as described above. Anappropriate sensor that has conventionally been known can be adopted forthis stroke sensor 33. For example, the stroke sensor 33 may be a typeof sensor that detects a stroke of the actuator 32 by capacitance orelectrical resistance that varies by the operation amount of theactuator 32, a type of sensor that detects the stroke of the actuator 32optically, or the like. In addition, instead of detecting the stroke ofthe actuator 32, a so-called ON/OFF sensor may output a signal at anadvanced end and a retracted end of the actuator 32.

As described above, the SOWC 17 can be engaged when the differentialrotation between the first clutch plate 24 and the second clutch plate25 is positive. In other words, in the state of the positivedifferential rotation of the SOWC 17, the strut 26 is fitted to andengaged with the pocket 29 at the position between the first clutchplate 24 and the second clutch plate 25. Accordingly, the torque can betransmitted between the first clutch plate 24 and the second clutchplate 25 via the strut 26. For this reason, if the strut 26 is operatedto be engaged with the pocket 29 in the state of the positivedifferential rotation of the SOWC 17, there is a case where the torqueis applied to the strut 26 that is in the middle of a path for the strut26 to be completely engaged at a specified position in the pocket 29,and thus the strut 26 is engaged with the pocket 29 at an improperposition. In such an improper engaged state, surface pressure that actson a contact portion between the strut 26 and the pocket 29 isincreased. As a result, the load applied to the strut 26 is possiblyincreased.

In view of this, the control device according to the invention that hasthe above power transmission mechanism as the subject is configured toexecute control, which will be described below, such that the strut 26is not engaged with the pocket 29 at the improper position during theengagement of the SOWC 17. FIG. 7 is a flowchart for illustrating anexample of such control. A routine shown in this flowchart of FIG. 7 isrepeatedly executed at specified short time intervals. In addition, inthe routine shown in this flowchart of FIG. 7, the control is executedwith an assumption that the vehicle Ve travels in the disengaged stateof the SOWC 17 and that the differential rotation speed of the SOWC 17is positive.

In the flowchart of FIG. 7, it is first determined whether the SOWC 17will be engaged (step S1). If a negative determination is made in thisstep S1 due to the lack of a request for engaging the SOWC 17, thisroutine is once terminated without executing control in the followingsteps.

On the contrary, if a positive determination is made in step S1 due tothe presence of the request for engaging the SOWC 17, a process proceedsto step S2. For example, in the example of the configuration shown inFIG. 1, when the vehicle Ve travels forward by the output of the engine1 and the output of the second motor 3, the rotation of the first motor2 and the rotation of the sun gear 5 are locked. In such a case, theSOWC 17 is engaged. Alternatively, in the example of the configurationshown in FIG. 3, when the overdrive state is set, the rotation of thering gear 22 in the overdrive mechanism 19 is locked. In such a case,the SOWC 17 is engaged.

In step S2, synchronous control is initiated. Here, the synchronouscontrol refers to a series of control of the rotational speed that isexecuted when the SOWC 17 is engaged. The synchronous control alsorefers to control in which the differential rotation speed of the SOWC17 is once maintained to be negative for the engagement of the SOWC 17and then is gradually increased to the positive side, so as to bring theSOWC 17 into an engageable state. More specifically, the differentialrotation speed of the SOWC 17 is synchronized with unlock-side targetdifferential rotation speed, and the rotation of the first motor 2 iscontrolled such that the differential rotation speed of the SOWC 17 ismaintained at the unlock-side target differential rotation speed for aspecified time period. The unlock-side target differential rotationspeed corresponds to a target value that is used when the differentialrotation speed of the SOWC 17 becomes negative (that is, on the unlockside). This unlock-side target differential rotation speed is set inadvance on the basis of a result of an experiment, a simulation, or thelike in consideration of a fluctuation in the rotational speed that iscaused by control disturbance, such as a fluctuation in torque of theengine 1 or input of disturbance torque, such that the differentialrotation speed of the SOWC 17 becomes negative even with occurrence ofsuch a fluctuation.

Furthermore, the above unlock-side target differential rotation speedcan be set by changing the value in accordance with a magnitude of thepredicted control disturbance. More specifically, the unlock-side targetdifferential rotation speed can be set such that the value thereof ischanged to be increased as the magnitude of the predicted controldisturbance is increased. For example, a map shown in FIG. 8A or FIG. 8Bcan be used to set the unlock-side target differential rotation speed.In an example shown in FIG. 8A, the unlock-side target differentialrotation speed is set such that an absolute value of the unlock-sidetarget differential rotation speed is increased as a throttle openingdegree of the engine 1 is increased. In the engine 1, the engine torqueis increased as the throttle opening degree is increased. Then, when theengine torque is increased, the fluctuation in torque is also increased.Accordingly, the fluctuation in the differential rotation speed of theSOWC 17 is also increased by the occurrence of the significantfluctuation in torque, just as described. In such a case, the absolutevalue of the unlock-side target differential rotation speed is increased(that is, the value of the unlock-side target differential rotationspeed is reduced on the negative side). Thus, even with the occurrenceof the fluctuation, the differential rotation speed of the SOWC 17 canbe maintained to be negative.

In addition, in an example shown in FIG. 8B, the unlock-side targetdifferential rotation speed is set such that the absolute value of theunlock-side target differential rotation speed is increased as an amountof increase in the throttle opening degree of the engine 1, that is, anamount of change of the throttle opening degree in a direction to beopened wider is increased. It is difficult to estimate the engine torquewhen the engine 1 is in a rapid transient state that the amount ofincrease in the throttle opening degree is large. Accordingly, adiscrepancy between the estimated engine torque and the actual enginetorque is possibly increased as the amount of increase in the throttleopening degree is increased. With such an increased discrepancy, thefluctuation in the differential rotation speed of the SOWC 17 ispossibly increased. Also in such a case, the absolute value of theunlock-side target differential rotation speed is increased (that is,the value of the unlock-side target differential rotation speed isreduced on the negative side). Thus, even with the occurrence of thefluctuation, the differential rotation speed of the SOWC 17 can bemaintained to be negative.

Once the synchronous control is initiated as described above, it isdetermined whether the differential rotation speed of the SOWC 17 hasreached actuator ON differential rotation speed (step S3). The actuatorON differential rotation speed is differential rotation speed at whichON control of the actuator 32 is initiated for the engagement of theSOWC 17 in the synchronous control of the SOWC 17. This actuator ONdifferential rotation speed is zero or a value close to zero.Furthermore, this actuator ON differential rotation speed is set as avalue that is lower than the lock-side differential rotation speed,which will be described below. This actuator ON differential rotationspeed is also set in advance on the basis of a result of an experiment,a simulation, or the like, for example, in consideration ofresponsiveness of the actuator 32. Noted that, in this step S3 of thecontrol, instead of the above actuator ON differential rotation speed,it can be determined whether the differential rotation speed of the SOWC17 has reached the unlock-side target differential rotation speed.

A negative determination is made in this step S3 if the differentialrotation speed of the SOWC 17 has not reached the actuator ONdifferential rotation speed. In this case, the process returns to stepS2, and the above synchronous control is continued. On the contrary, apositive determination is made in step S3 if the differential rotationspeed of the SOWC 17 has reached the actuator ON differential rotationspeed. In this case, the process proceeds to step S4. Then, the abovesynchronous control is continued, and the ON control of the actuator 32is initiated.

If the ON control of the actuator 32 is initiated, it is determinedwhether a stroke (an operation) of the actuator 32 is completed (stepS5). Once the ON control is initiated, the actuator 32 is operated tocancel pressing of the strut 26, so as to project the strut 26 to thesecond clutch plate 25 side. Accordingly, in this step S5, the operatingstate of the actuator 32 can be determined on the basis of the detectionsignal of the stroke sensor 33 or the ON/OFF sensor.

A negative determination is made in this step S5 if the operation of theactuator 32 for engagement of the engagement mechanism 23 has not beencompleted. In this case, the process returns to step S4, and the abovesynchronous control and the ON control of the actuator 32 are continued.

A positive determination is made in step S5 if the operation of theactuator 32 for the engagement of the engagement mechanism 23 has beencompleted. In this case, the process proceeds to step S6. Then, it isdetermined whether a specified time period has elapsed since theinitiation of the ON control of the actuator 32. This specified timeperiod is estimated and set in advance as time required for the strut 26to move to a specified position for engagement by the operation of theactuator 32 in consideration of the responsiveness of the actuator 32and the operation of the strut 26. This specified time period is alsoset in advance on the basis of a result of an experiment, a simulation,or the like, for example.

A negative determination is made in this step S6 if the specified timeperiod has not elapsed. In this case, the process returns to step S4,and the above synchronous control and the ON control of the actuator 32are continued.

If a positive determination is made in step S6 due to a lapse of thespecified time period, a process proceeds to step S7. Then, lockrotation control is initiated. This lock rotation control is control inwhich the differential rotation speed of the SOWC 17, which ismaintained at the unlock-side differential rotation speed on thenegative side (that is, the unlock side), is increased to be thedifferential rotation speed on the positive side (that is, the lockside), so as to bring the SOWC 17 into the engageable state. Morespecifically, the rotation of the first motor 2 is controlled such thatthe differential rotation speed of the SOWC 17 is a value on thepositive side.

Once the lock rotation control is initiated in step S7 as describedabove, the differential rotation speed of the SOWC 17 is then increasedto the lock-side target differential rotation speed and maintained atthe lock-side target differential rotation speed (step S8). Thelock-side target differential rotation speed is the differentialrotation speed at which the differential rotation of the SOWC 17 is thepositive differential rotation and at which SOWC 17 can be engaged. Inaddition, as shown in FIG. 9, this lock-side target differentialrotation speed is set as a value that is lower than a lower limit ofratchet minimum differential rotation speed, which will be describedbelow.

As described above, the engagement mechanism 23 of this SOWC 17 isbrought into the engageable state when the differential rotation of theSOWC 17 is the positive differential rotation. In addition to the above,this SOWC 17 is provided with a ratchet function that inhibits theengagement between the strut 26 and the pocket 29 when the differentialrotation speed is excessively high. More specifically, this SOWC 17 isconfigured that the strut 26 is flicked by an opening portion of thepocket 29 and thus cannot be engaged with the pocket 29 (that is, anratchet action is exerted) when the differential rotation speed of theSOWC 17 is higher than specified differential rotation speed. Thespecified differential rotation speed in this case is the ratchetminimum differential rotation speed. Accordingly, the SOWC 17 isconfigured that it can be engaged (locked) when the differentialrotation speed thereof is lower than the ratchet minimum differentialrotation speed and that it is ratcheted and thus cannot be engaged whenthe differential rotation speed thereof is higher than the ratchetminimum differential rotation speed. If the SOWC 17 is engaged at thehigh differential rotation speed, the impact caused by the engagement ofthe strut 26 and the pocket 29 becomes substantial. However, due to theprovision of the ratchet function as described above, the impact orshock during the engagement can be suppressed.

Furthermore, a fluctuation in the ratchet minimum differential rotationspeed is unavoidable due to a structure of the engagement mechanism 23.In other words, when the differential rotation speed of the SOWC 17 isclose to the ratchet minimum differential rotation speed, there is acase where the SOWC 17 can be either locked or ratcheted. For thisreason, as shown in FIG. 9, an upper limit of the ratchet minimumdifferential rotation speed and a lower limit of the ratchet minimumdifferential rotation speed are set in this lock rotation control. Whenthe differential rotation speed of the SOWC 17 is higher than the upperlimit of the ratchet minimum differential rotation speed, the SOWC 17 isalways ratcheted to prevent the engagement thereof. On the contrary,when the differential rotation speed of the SOWC 17 is lower than thelower limit of the ratchet minimum differential rotation speed, the SOWC17 is always engaged.

If the lock rotation control is executed in step S7 and step S8, it isdetermined whether the differential rotation speed of the SOWC 17 islower than engagement stop differential rotation speed (step S9). Asshown in FIG. 9, this engagement stop differential rotation speed is setas a value that is higher than the upper limit of the above ratchetminimum differential rotation speed. Accordingly, a negativedetermination is made in this step S9 if the differential rotation speedof the SOWC 17 is equal to or higher than the engagement stopdifferential rotation speed. In this case, the process proceeds to stepS10, and engagement stop control for stopping a series of thesynchronous control, which includes the above lock rotation control, isexecuted. Then, this routine is terminated once.

On the contrary, a positive determination is made in step S9 if thedifferential rotation speed of the SOWC 17 is lower than the engagementstop differential rotation speed. In this case, the process proceeds tostep S11. Then, it is determined whether the differential rotation speedof the SOWC 17 is lower than retry differential rotation speed. As shownin FIG. 9, this retry differential rotation speed is set as a value thatis lower than the upper limit of the above ratchet minimum differentialrotation speed and is also higher than the lower limit of the ratchetminimum differential rotation speed. Accordingly, when the differentialrotation speed of the SOWC 17 is higher than this retry differentialrotation speed, a possibility that the SOWC 17 is ratcheted and thuscannot be engaged is increased. Thus, a negative determination is madein this step S11 if the differential rotation speed of the SOWC 17 isequal to or higher than this retry differential rotation speed. In thiscase, the process returns to step S2, and the above-describedsynchronous control is executed again. In other words, the differentialrotation speed of the SOWC 17 is returned to the unlock-side targetdifferential rotation speed that is set on the negative side, and theseries of the control from the synchronous control in step S2 onward isexecuted again.

On the contrary, a positive determination is made in this step S11 ifthe differential rotation speed of the SOWC 17 is lower than this retrydifferential rotation speed. In this case, the process proceeds to stepS12. Then, it is determined whether the differential rotation speed ofthe SOWC 17 becomes substantially zero. In other words, it is determinedin this step S12 whether the SOWC 17 has become engaged. It can bedetermined that the SOWC 17 has become engaged, in the case where thedifferential rotation speed of the SOWC 17 that is maintained at thelock-side target differential rotation speed becomes substantially zero.Accordingly, a negative determination is made in this step S12 if thedifferential rotation speed of the SOWC 17 has not become substantiallyzero. In this case, the process returns to step S8, and the lockrotation control, in which the differential rotation speed of the SOWC17 becomes and is maintained at the lock-side target differentialrotation speed, is continued.

A positive determination is made in step S12 if the differentialrotation speed of the SOWC 17 has become substantially zero. In thiscase, the process proceeds to step S13. That is, if it is determinedthat the SOWC 17 has become engaged, the process proceeds to step S13.Then, transition of torque from the first motor 2 to the SOWC 17 isinitiated. More specifically, the first motor 2 is controlled such thatthe output torque thereof becomes zero. For example, in the example ofthe configuration shown in FIG. 1, the output torque of the first motor2 becomes zero in a state that the rotation of the first motor 2 and therotation of the sun gear 5 are locked by the SOWC 17. Alternatively, inthe example of the configuration shown in FIG. 3, the output torque ofthe first motor 2 becomes zero in a state that the rotation of the ringgear 22 in the overdrive mechanism 19 is locked by the SOWC 17. Then,this routine is terminated once.

A time chart in FIG. 9 shows an example of the change in thedifferential rotation speed of the SOWC 17 when the above control shownin the flowchart in FIG. 7 is executed. Once a determination forswitching the SOWC 17 to the engaged state is established in a statethat the vehicle Ve travels in the disengaged state of the SOWC 17 (timet1), the above-described synchronous control is initiated. Then, therotation of the first motor 2 is controlled such that the differentialrotation speed of the SOWC 17 is reduced to the negative side (time t2).

The differential rotation speed of the SOWC 17 is gradually reduced tothe negative side and eventually reaches the actuator ON differentialrotation speed, which is set as a specified value close to zero. At thistime, the actuator 32 is controlled to be ON (time t3). Thereafter, onceit is detected by the detection signal of the stroke sensor 33 or thelike that the stroke of the actuator 32 is completed (time t4), a timeris actuated. Then, the lock rotation control is initiated at a timepoint (time t5) when a specified time period has elapsed since thecompletion of the stroke of the actuator 32 is detected. The specifiedtime period set here is a time period that is estimated as time requiredfor the operation of the actuator 32 to be completed and for the strut26 to move to the specified position for engagement, as described above.

Meanwhile, while the operation of the actuator 32 is controlled asdescribed above, the differential rotation speed of the SOWC 17 isgradually reduced to the unlock-side target differential rotation speedthat is set on the negative side. Then, once the differential rotationspeed of the SOWC 17 becomes the unlock-side target differentialrotation speed, the rotation of the first motor 2 is subject to feedbackcontrol such that the differential rotation speed is maintained at theunlock-side target differential rotation speed. This control formaintaining the differential rotation speed of the SOWC 17 at theunlock-side target differential rotation speed is continued until theabove time t5, that is, until a time point at which the completion ofthe stroke of the actuator 32 is estimated. Accordingly, the operationof the strut 26 for the engagement of the SOWC 17 is always performed inthe state that the differential rotation speed of the SOWC 17 isnegative. Thus, the strut 26 can be operated from the second clutchplate 25 of the SOWC 17 without being applied with the torque. As aresult, such a situation that the strut 26 and the pocket 29 are engagedat an improper position that is located in a middle of a path for thestrut 26 to be engaged at a specified position in the pocket 29 can beavoided.

Once the lock rotation control is initiated at the time t5, the rotationof the first motor 2 is controlled such that the differential rotationspeed of the SOWC 17 is increased to the lock-side target differentialrotation speed that is set on the positive side. Then, once thedifferential rotation speed of the SOWC 17 becomes the lock-side targetdifferential rotation speed, the rotation of the first motor 2 issubject to feedback control such that the differential rotation speed ismaintained at the lock-side target differential rotation speed. Asdescribed above, the lock-side target differential rotation speed is setas the value on the positive side that is lower than the lower limit ofthe ratchet minimum differential rotation speed at which the SOWC 17 isalways engaged. For this reason, the SOWC 17 can be smoothly shifted tothe engaged state in the state that the differential rotation speedthereof is maintained at the lock-side target differential rotationspeed.

Then, the engagement of the SOWC 17 is completed, and thus thedifferential rotation speed of the SOWC 17 becomes zero (time t6).Accordingly, it can be determined that the engagement of the SOWC 17 iscompleted by monitoring the change of the differential rotation speed ofthe SOWC 17. Once it is determined that the engagement of the SOWC 17 iscompleted, just as described, the torque transition from the first motor2 to the SOWC 17 is initiated (time t7). More specifically, the firstmotor 2 is controlled such that the output torque thereof becomes zero.

As it has been described specifically so far, according to the controldevice of the invention, in the case where the SOWC 17, the differentialrotation speed of which is positive, is switched from the disengagedstate to the engaged state, the rotation of the first motor 2 iscontrolled such that the differential rotation once becomes the negativedifferential rotation. Then, the actuation mechanism 27 of the SOWC 17is actuated such that the projection of the strut 26 to the secondclutch plate 25 at the position between the first clutch plate 24 andthe second clutch plate 25 is permitted in the state that thedifferential rotation is the negative differential rotation. When thedifferential rotation of the SOWC 17 is the negative differentialrotation, the torque is not transmitted between the first clutch plate24 and the second clutch plate 25. Thus, no load is applied to the strut26. In other words, the strut 26 can easily be operated. Thus, the strut26 can easily be operated and reliably be engaged at a specifiedposition by setting such a state that the projection of the strut 26 tothe second clutch plate 25 is permitted as described above in the statethat the differential rotation is the negative differential rotation.Therefore, the SOWC 17 in the disengaged state can appropriately andreliably be switched to the engaged state.

In the above-described specific example, the configuration in which theSOWC 17 is used as a brake for selectively stopping the rotation of thesun gear 5 or the ring gear 22 is described. Meanwhile, in thisembodiment, the SOWC 17 can also be configured such that it is used as aclutch for selectively transmitting the torque between the two rotarymembers. Such an example is shown in FIG. 10. A part of theconfiguration shown in FIG. 1, which is described above, is modified forthis example of the configuration shown in FIG. 10. More specifically,instead of the engine 1, the output gear 8 is coupled to the carrier 6in the planetary gear mechanism, which constitutes the power splitmechanism 4. In addition, instead of the output gear 8, the engine 1 iscoupled to the ring gear 7. Furthermore, the SOWC 17 shown in this FIG.10 is configured to selectively couple the ring gear 7 (the engine 1)and the sun gear 5. A direction of engagement of the SOWC 17 in thiscase is a direction in which the torque is transmitted from the engine 1to the sun gear 5 in the positive rotational direction. The rest of theconfiguration is the same as the configuration shown in FIG. 1.Accordingly, components shown in this FIG. 10 are denoted by the samereference numerals as those used in FIG. 1, and the description thereofwill not be made.

In the power transmission mechanism that is configured as shown in FIG.10, the HV mode (or the power split mode) and a direct connection mode(or the parallel mode) can be set. In the HV mode, the power output bythe engine 1 is divided by the output gear 8 and the first motor 2. Inthe direct connection mode, a differential action of the power splitmechanism 4 is stopped, and the entire power split mechanism 4 isintegrated for rotation. The SOWC 17 shown in this FIG. 10 is engagedwhen the vehicle Ve travels forward in the above direct connection mode.

FIG. 11 includes collinear diagrams on the planetary gear mechanism thatconstitutes the power split mechanism 4 shown in FIG. 10. A top diagramin FIG. 11 indicates a state that the vehicle Ve travels forward in theHV mode with the SOWC 17 being disengaged. In this state shown in thetop diagram in FIG. 11, the torque in the positive rotational directionof the engine 1 is transmitted to the ring gear 7. Meanwhile, reactiontorque in the reverse rotational direction that is generated inconjunction with the travel of the vehicle Ve acts on the carrier 6.Accordingly, the torque in the reverse rotational direction acts on thesun gear 5. This corresponds to the torque in the positive rotationaldirection of the engine 1 with respect to the sun gear 5. However, sincethe SOWC 17 is disengaged, the sun gear 5 rotates reversely as shown inthe top diagram in FIG. 11, for example. In this case, the first motor 2that is coupled to this sun gear 5 functions as the electrical powergenerator and applies the torque in the positive rotational direction(the upward direction in the top diagram in FIG. 11) as the reactionforce to the sun gear 5. As a result, the torque of the engine 1 isamplified and transmitted to the output gear 8, which is coupled to thecarrier 6. In addition, the first motor 2 controls the speed of theengine 1 to the speed at which the excellent fuel efficiency can berealized. Furthermore, the electrical power generated in the first motor2 is supplied to the second motor 3. Then, the second motor 3 functionsas the motor. In other words, some of the power of the engine 1 that hasbeen converted to the electrical power is converted to the mechanicalpower again, and is transmitted to the drive wheels 14.

A second diagram from the top in FIG. 11 indicates a transient state (atransition state) in which the SOWC 17 is switched between the stateshown in the above top diagram in FIG. 11 and a state shown in the thirddiagram from the top in FIG. 11, which will be described below. In otherwords, the second diagram from the top in FIG. 11 indicates thetransient state when the SOWC 17 is switched from the disengaged state(free) to the engaged state (locked) in which the SOWC 17 restricts therelative rotation between the sun gear 5 and the engine 1. In this stateshown in the second diagram from the top in FIG. 11, the first motor 2functions as the motor and rotates the sun gear 5 in the positiverotational direction. At this time, the rotational speed of the sun gear5 exceeds the speed of the engine 1. In other words, the first motor 2is controlled such that the engine 1 rotates in the reverse rotationaldirection (the negative rotation) relative to the sun gear 5. Suchrelative rotation is an example of the differential rotation in theinvention, and in this state shown in the second diagram from the top inFIG. 11, the negative differential rotation is produced. In other words,the SOWC 17 does not transmit the torque. Thus, when the engagementcontrol of the SOWC 17 is executed in this state, the torque is notapplied to the strut 26 of the SOWC 17. Noted that, in this state shownin the second diagram from the top in FIG. 11, the direction of thedifferential rotation, the direction of the torque of the first motor 2,and the rotational direction of the first motor 2 are opposite fromthose in the examples shown in the collinear diagrams of above-describedFIG. 2 and FIG. 4. However, as described above, the SOWC 17 shown inFIG. 10 is configured such that the differential rotation produced inthis state shown in the second diagram from the top in FIG. 11 becomesthe negative differential rotation. Accordingly, the same control as thecontrol example shown in the flowchart of FIG. 7 is executed so that theSOWC 17 can reliably and appropriately be engaged.

A third diagram from the top in FIG. 11 indicates a state that thevehicle Ve travels forward in the direct connection mode. In the forwardtravel state, as described above, the torque in the direction to causethe reverse rotation of the sun gear 5 acts thereon, and the engine 1attempts to rotate in the positive rotational direction relative to thesun gear 5. Accordingly, when the SOWC 17 is controlled to be in theengaged state, the above-described strut 26 is interposed (meshed)between the housing section 28 of the first clutch plate 24 and thepocket 29 of the second clutch plate 25, and thus the sun gear 5 and theengine 1 are coupled to rotate integrally in the positive rotationaldirection. As a result, since the two rotary elements are integrated,the entire power split mechanism 4 rotates integrally. In other words,the engine 1 is directly connected to the output gear 8.

Noted that, in the configuration shown in FIG. 10, the first motor 2 iscoupled to the first clutch plate 24 of the SOWC 17, and the rotationalspeed of the first clutch plate 24 is controlled by the first motor 2.Meanwhile, in the above-described configuration shown in FIG. 1, thefirst motor 2 is coupled to the second clutch plate 25 of the SOWC 17,and the rotational speed of the second clutch plate 25 is controlled bythe first motor 2. In addition, in the above-described configurationshown in FIG. 3, the first motor 2 is coupled to the second clutch plate25 of the SOWC 17 via the overdrive mechanism 19, and the rotationalspeed of the second clutch plate 25 is controlled by the first motor 2.As described above, the first motor 2 is configured that it can controlthe rotational speed of either clutch member of the first clutch plate24 or the second clutch plate 25 of the SOWC 17, and is an example ofthe motor of the invention.

Furthermore, the invention can be applied to a control device for apower transmission mechanism that includes a stepped transmission or acontinuously variable transmission other than the power transmissionmechanism that is installed in the hybrid vehicle Ve as described above.Thus, the motor in the invention may be a motor for controlling the SOWConly.

What is claimed is:
 1. A control system for a vehicle, the controlsystem comprising: a selectable one-way clutch including a first clutchmember, a second clutch member, a strut, and a switching mechanism, thefirst clutch member and the second clutch member configured to rotaterelatively to each other, at least a part of the strut configured to beoperated such that the part of the strut is projected from a firstclutch member side to a second clutch member side, the switchingmechanism configured to selectively set a first state and a secondstate, the first state being a state that the switching mechanismpermits a projection of the strut to the second clutch member side, andthe second state being a state that the switching mechanism inhibits theprojection of the strut, the selectable one-way clutch configured to beswitched between an engaged state and a disengaged state, the engagedstate being a state that restricts a relative rotation in either apositive rotational direction or a reverse rotational direction in thefirst state with engaging the part of the strut with a part of thesecond clutch member, and the disengaged state being a state thatpermits the relative rotation in both of the positive rotationaldirection and the reverse rotational direction in the second statewithout projecting the strut to the second clutch member side; a motorconfigured to control a rotational speed of either the first clutchmember or the second clutch member; and an electronic control unitconfigured to (i) produce differential rotation by controlling therotational speed by the motor, the differential rotation includingpositive differential rotation and negative differential rotation, thepositive differential rotation being the relative rotation in which therelative rotation is restricted in the engaged state, and the negativedifferential rotation being the relative rotation in which the relativerotation is permitted in the engaged state, (ii) execute followingprocesses in an order of (1) to (4) when the electronic control unitswitches the selectable one-way clutch from the disengaged state to theengaged state: (1) controlling the motor such that the differentialrotation becomes the negative differential rotation; (2) switching theselectable one-way clutch from the second state to the first state suchthat the part of the strut is projected from the first clutch memberside to the second clutch member side in a state that the differentialrotation is the negative differential rotation; (3) controlling themotor such that the differential rotation becomes the positivedifferential rotation; and (4) engaging the part of the strut with thepart of the second clutch member in a state that the differentialrotation is the positive rotational direction; (iii) set a first targetdifferential rotation speed, the first target differential rotationspeed is a target value of a differential rotation speed that is usedwhen the electronic control unit controls the motor such that thedifferential rotation becomes the negative differential rotation, and(iv) control the motor such that the differential rotation speed ismaintained at the first target differential rotation speed until thepart of the strut is projected to the second clutch member side.
 2. Thecontrol system according to claim 1, wherein the switching mechanismincludes an actuator that is configured to operate the strut, and theelectronic control unit is configured to initiate actuation of theactuator before the differential rotation speed reaches the first targetdifferential rotation speed, when the electronic control unit sets thefirst state in the state that the differential rotation is the negativedifferential rotation after the electronic control unit controls themotor such that the differential rotation becomes the negativedifferential rotation.
 3. The control system according to claim 1,wherein the switching mechanism includes an actuator that is configuredto operate the strut, and the electronic control unit is configured toinitiate actuation of the actuator, when a differential rotation speedis zero or positive value that is close to zero, when the electroniccontrol unit sets the first state in the state that the differentialrotation is the negative differential rotation after the electroniccontrol unit controls the motor such that the differential rotationbecomes the negative differential rotation.
 4. The control systemaccording to claim 1, wherein the switching mechanism includes anactuator that is configured to operate the strut, a second targetdifferential rotation speed is set as a target value of a differentialrotation speed that is used when the electronic control unit controlsthe motor such that the differential rotation becomes the positivedifferential rotation, and the electronic control unit is configured toexecute the following processes in an order of (i) to (v): (i) settingthe first state by actuating the actuator such that the part of thestrut is projected to the second clutch member side in the state thatthe differential rotation speed is maintained at the first targetdifferential rotation speed; (ii) controlling the motor such that thedifferential rotation becomes the positive differential rotation; (iii)engaging the part of the strut with the part of the second clutch memberin the state that the differential rotation is the positive differentialrotation; (iv) controlling the motor after the actuation of the actuatoris completed and an operation of the part of the strut to be projectedto the second clutch member side is completed, such that thedifferential rotation speed is increased to the second targetdifferential rotation speed; and (v) controlling the motor such that thedifferential rotation speed is maintained at the second targetdifferential rotation speed until engagement of the part of the strutand the part of the second clutch member is completed.
 5. The controlsystem according to claim 1, wherein an absolute value of the firsttarget differential rotation speed is set higher as a magnitude ofpredicted control disturbance is increased.
 6. The control systemaccording to claim 1, further comprising: an internal combustion engine;a drive wheel; and a power transmission mechanism including a fixedsection and a first differential mechanism, wherein either the firstclutch member or the second clutch member is coupled to the fixedsection, the fixed section is configured not to rotate or move, thefirst differential mechanism includes a first rotary element, a secondrotary element, and a third rotary element, the first rotary element,the second rotary element, and the third rotary element are configuredto perform a differential action with respect to each other, theinternal combustion engine is coupled to the first rotary element, themotor and the other one of the first clutch member and the second clutchmember are coupled to the second rotary element, and the firstdifferential mechanism is configured to output torque from the thirdrotary element to the drive wheel.
 7. The control system according toclaim 1, further comprising: an internal combustion engine; a drivewheel; and a power transmission mechanism including a fixed section, afirst differential mechanism, and a second differential mechanism,wherein either one of the first clutch member and the second clutchmember is coupled to the fixed section, the fixed section is configurednot to rotate or move, the first differential mechanism includes a firstrotary element, a second rotary element, and a third rotary element, thefirst rotary element, the second rotary element, and the third rotaryelement are configured to perform a differential action with respect toeach other, the internal combustion engine is coupled to the firstrotary element, the motor is coupled to the second rotary element, thefirst differential mechanism is configured to output torque from thethird rotary element to the drive wheel, the second differentialmechanism includes a fourth rotary element, a fifth rotary element, anda sixth rotary element, the fourth rotary element, the fifth rotaryelement, and the sixth rotary element are configured to perform thedifferential action with respect to each other, the first rotary elementis coupled to the fourth rotary element, the second rotary element iscoupled to the fifth rotary element, the other one of the first clutchmember and the second clutch member is coupled to the sixth rotaryelement, and the fifth rotary element is configured to rotate in anopposite direction from a rotational direction of the fourth rotaryelement by stopping rotation of the sixth rotary element.